JP3112491B2 - Auto focusing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto-focusing system, and more particularly to an auto-focusing system which detects an in-focus state on the basis of a change in contrast information of an image sensor output.

[0002]

2. Description of the Related Art As one of conventional automatic focusing methods, contrast information of a subject indicating a degree of focusing is obtained based on a video signal when an in-focus lens is extended or retracted in an imaging apparatus using an imaging device. Then, a peak value of the value is obtained, a position indicating the peak value is determined as a focus position, and a focus lens is driven to the position (see Japanese Patent Application Laid-Open No. 63-157578; JP-A-63-2
No. 6,2971, etc.). This focusing method is called a “hill climbing method”. For example, an NHK technical research report (Showa 4)
0, Vol. 17, No. 1, Total No. 86, pp. 21-37).

In the focus detection apparatus using the hill-climbing method, each value of contrast information sequentially obtained by extending or retracting a lens is a predetermined natural number m times smaller than the maximum value in comparison with the past. When the lens position is recognized, the lens position showing the maximum value (hereinafter referred to as the first lens position) is displayed.
Has been previously proposed by the present applicant as Japanese Patent Application No. 2-401327.

[0004]

In the focus adjustment method proposed in Japanese Patent Application No. 2-401327, when a predetermined natural number m is increased, as shown in FIG. For example, when the contrast value of a subject is flat as a whole, or when noise such as flicker or camera shake as shown in FIG.
This is effective because focusing accuracy is improved. However, in the case of a telephoto subject whose contrast value changes as shown in FIG. 13, for example, the predetermined natural number m may be reduced, but m is fixed. The number of steps up to this point is too large and the focusing speed becomes slow. Therefore, the release time lag becomes long, and there is a possibility that a shutter chance is missed.

Conversely, if the predetermined natural number m is reduced, the focusing speed becomes faster when the peak point of the contrast value can be clearly seen as shown in FIG.
In the case where the contrast value as shown in FIG. 11 is entirely flat, or in the case where noise such as flicker or camera shake is superimposed as shown in FIG. 12, false focusing occurs and the focusing accuracy is reduced. So there is room for improvement.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an accurate and efficient combination according to the state of an object such as flicker, camera shake, telephoto or wide, which has a correlation with image sharpness. An object of the present invention is to provide an auto-focusing system capable of being driven by a focus.

[0007]

SUMMARY OF THE INVENTION An auto-focusing system according to the present invention comprises a signal corresponding to the sharpness of an image obtained by the focusing lens which is obtained corresponding to each lens position in the gradual driving of the focusing lens. An auto-focusing system that drives the focusing lens to a position determined to indicate a predetermined natural number m according to a state of a predetermined object having a correlation with image sharpness; From the first lens position when the signal level corresponding to the sharpness of the image shows the maximum value in comparison with the past in the course of the progressive driving of the focusing lens, it is continuously performed m times determined by the first means. When the focusing lens is gradually driven to reach the second lens position, the signal level becomes the maximum value at each of the m lens positions. A second means for judging that the signal level corresponding to the sharpness of the image by the focusing lens substantially shows a peak value when the first lens position is lower than the above. And

[0008]

In this auto-focusing system, the first lens position is determined when the signal level corresponding to the sharpness of the image, that is, the contrast value Cn indicates the maximum value in comparison with the past in the course of the progressive driving of the focusing lens. FIG. 14 shows the number n of lens feeding steps to the second lens position that passes through the first lens position and provides a predetermined natural number m times a contrast value lower than the contrast value at the first lens position. As shown,
N according to the state of a given object correlated with the sharpness of the image
= 2 or n = 5.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the illustrated embodiments. The first embodiment of the present invention is shown in FIG. 2, the second embodiment is shown in FIGS. 5 and 6, the third embodiment is shown in FIGS.
The embodiment is configured as shown in the respective flowcharts of FIGS. 9 and 10. However, since the configuration on the hardware side is the same, FIG. 1 showing the block configuration will be described first.

As shown in FIG. 1, an image pickup apparatus having a built-in auto-focusing system according to the present invention mainly performs an image pickup lens 1, a half mirror 10, an image pickup element 2, an image pickup signal amplification and a sample hold processing. Imaging processing circuit 3
B. extracting the contrast value, which is the contrast information, from the image pickup signal. P. F. (Band pass filter) circuit 5 and analog / contrast information
A first A / D conversion circuit 6 for digital conversion, a CPU,
An arithmetic processing circuit 7 including a ROM, a RAM, and the like;
A motor 8 for driving the photographing lens 1, a motor drive circuit 9 for the motor 8, a photometric element 11, and a second A / D conversion circuit 12 for A / D converting photometric information obtained by the element 11 And a video recording / reproducing system (not shown).

The operation of the imaging apparatus having the above configuration is as follows. First, the subject light is taken in through the imaging lens 1, the subject light is split by the half mirror 10, and the respective light receiving surfaces of the imaging element 2 and the photometry element 11 are separated. Each image is formed as a subject image on the top. An output signal from the image sensor 2 is output to an image processing circuit 3
At the output terminal 4 and B. P. Output to the F circuit 5. And
The signal is output from the output terminal unit 4 to a recording / reproducing system circuit. B. P. In the F circuit 5, a predetermined high frequency component is extracted as a contrast value. Further, the data is converted into a digital value by the first A / D conversion circuit 6 and is taken into the RAM of the arithmetic processing circuit 7. The photometric information obtained by converting the light quantity into the voltage by the photometric element 11 is the second A / A
The data is converted into a digital value by the D conversion circuit 12, and is taken into the RAM of the arithmetic processing circuit 7. The arithmetic processing circuit 7 includes means for recognizing the peak point of the contrast value, means for determining the value of a predetermined natural number m, and means for determining focus, and further includes a focus detection operation and a focus operation. Control means for driving the motor 8 via the motor drive circuit 9 to move the photographing lens 1 to a predetermined position are incorporated.

Next, a processing operation including a focusing process in the automatic focusing system according to the first embodiment of the present invention will be described with reference to a flowchart of FIG. in this case,
In the focus detection processing, detection is performed in the lens extension direction. In addition, the variables appearing in the flowchart will be described. N is the number of steps indicating the current lens extension position, and s is the first number.
The number of detections when the value of the contrast information from the lens position to the second lens position is lower than the past maximum value CMAX is hereinafter referred to as the low value detection number. Further, the object brightness is divided into three types of A, B, and C, and A>B> C in the order of the brightness. Further, m is a predetermined natural number that is correlated with the sharpness of the image, for example, Mmax, Mtyp, Mmin as a predetermined natural number that can be varied according to the state of the subject luminance, flicker, or the like.
, And Mmax>Mtyp> Mmin.

In FIG. 2, when this flow is started, the number of stages n is reset to the initial value, that is, the most indented ∞ position (step S116). Then, the luminance information of the object is checked (step S117). If it is bright luminance A, the minimum value Mmin is set to a predetermined natural number m (step S118). If it is intermediate luminance B, the intermediate value Mtyp is made (step S119). The maximum value Mmax is set (step S120), and the process proceeds to step S101.

In step S101, the contrast value Cn at the stage number n indicating the current lens extension position is taken into the arithmetic processing circuit 7. Then, in step S102, the motor 8 is driven forward by one step to rotate the photographing lens 1. Similarly, in step S103, the number of steps n at the current lens extension position
The arithmetic processing circuit 7 calculates the contrast value Cn + 1 at +1
Take in. Then, in step S104, the contrast value Cn is compared with Cn + 1. If Cn + 1 is smaller, it is determined that the contrast value has entered the descending region of the hill-climbing process, and the process proceeds to step S105. If the contrast is not small, it is determined that the region where the contrast value is still increasing continues, and the process jumps to step S106. That step
In step S106, the number n of stages is incremented, and the process returns to step S102.

On the other hand, when the process proceeds to step S105, the number of times of low value detection s is set to 1, and the maximum value C is set at step S107.
Read the value Cn into max. In step S108, which is a means for recognizing the number of times, the number of times of low value detection s is compared with a predetermined natural number m. If the value s has not yet reached m, the flow proceeds to step S109. However, when the values s and m are equal, the low value detection has been performed the set number of times, and the process jumps to step S115 assuming that the contrast value peak point has been detected. Then, after executing a focusing processing subroutine described later, this processing ends.

In step S109, the motor 8 is further driven forward by one step to extend the lens 1. Step S110
And the contrast value C at the number of steps n + 2 at the current lens position
n + 2 is taken into the arithmetic processing circuit 7. And step
In step S111, the contrast value Cmax is compared with Cn + 2. If Cmax is larger, the process proceeds to step S112 to continue the low value detection. Also, if not big,
That is, when the current contrast value is larger than the past maximum value, it is determined that the contrast value has risen again, and the process jumps to step S114. Then, the number of stages n is incremented twice, and the process returns to step S102. When the process proceeds to step S112, the number of times of low value detection s is incremented, and the number of stages n is also incremented in step S113. Then, the process returns to step S108, and the detection operation is repeated again.

The subroutine focusing process called in step S115 corresponds to the focusing process A shown in FIG. In this process, in step S121, the position of the step number corresponding to the past maximum value Cmax of the contrast value rewritten in step S107 is regarded as the in-focus position, and the photographing lens 1 is moved to that position. Then, the process returns from this subroutine.

As a modification of the focusing process A, a focusing process B
Can be suggested. In the case of this modification as well, focusing processing is similarly performed based on the lens position data corresponding to the maximum value Cmax. In this case, another focusing processing operation is executed in step S123 shown in FIG. You. A drive system having mechanical backlash correction processing of a lens drive system can be applied as another device for the focusing operation. In this case, the focus position is set by shifting the lens position by the amount of backlash during driving.

In the first embodiment, the peak point of the contrast value is not determined only by a change in the contrast value for each single pixel, but is recognized as the peak point when a low value is detected a predetermined natural number m times. Then, the predetermined natural number m is changed according to subject luminance information which is a parameter affecting the focusing operation. (Refer to steps S117 to S120 above.) Therefore, unlike the conventional focusing device, the recognition of a low value is not compared with the immediately preceding value, but the comparison of the contrast value with the past maximum value is always performed. Are not uniformly reduced but tend to decrease, it is added to the number of times that a low value is detected. And
As shown in FIG. 11, the AF accuracy is increased by increasing the predetermined natural number m at the time of low luminance where the value change is small. On the other hand, when the luminance is bright as shown in FIG. 13, the predetermined natural number m is reduced to reduce the release time lag. As a result, the peak point or the fact that the peak point has been exceeded can be detected accurately and quickly.

Although the luminance of the subject is measured by the photometric device 11, it may be obtained from the image sensor 2.

Next, a second embodiment of the present invention will be described with reference to FIGS. Although FIGS. 5 and 6 are originally one flowchart, steps S122 and S101 are performed due to the space of the description.
Are described separately. In the first embodiment, only the subject brightness is considered as a parameter affecting the focusing operation. On the other hand, in the second embodiment, noise due to flicker of the light source such as flicker is considered in addition to the subject brightness. The points are different.

That is, the photometric information obtained by the photometric element 11 shown in FIG. 1 is converted into a digital value by the second A / D conversion circuit 12 and applied to the arithmetic processing circuit 7. Check for flicker (step S12
1) When a flicker is present, a predetermined natural number m is doubled as compared with a case where there is no flicker (step S122). Except for this point, there is no difference from the first embodiment,
The same steps are denoted by the same step numbers, and description thereof is omitted.

Therefore, according to the second embodiment, the aforementioned FIG.
Focus detection can be performed accurately even when flicker noise as shown in FIG. 2 is superimposed.

Next, a third embodiment of the present invention will be described with reference to FIGS. Although FIGS. 7 and 8 are originally one flowchart, steps S 203 and S 204
Are described separately.

The focus detection processing operation of the third embodiment is different from that of the second embodiment in that a limiter function for a lens extension position is added to the second embodiment. That is, in the operation of checking the contrast value by extending the focusing lens, the closest ending position within the lens adjustable range (hereinafter referred to as the number of the closest extending steps) without reaching the peak point Cmax indicating the maximum value of the hill-climbing curve compared with the past. Error processing is performed when n max is reached, and the peak position Cma of the hill-climbing curve is also set.
x, and entered the descending region, but the number n m of closest feeding stages without the number of times of low value detection s reaching the predetermined natural number m
After reaching ax, the normal focusing state is performed.

Referring to FIGS. 7 and 8, when this flow starts, first, the focusing lens is initialized to a super-∞ position further depressed from the {position (step S201), and the number of steps n is cleared (step S202). Next step S117 ~
In S122, the predetermined natural number m is corrected using parameters that affect the focusing operation as subject brightness and flicker. However, since this point is completely the same as in the above-described second embodiment, the same step numbers are given and the description is given. Omitted.

Steps S203 to S207 and S209 to S211
Steps S101 to S108 in the second embodiment are the same as those in the second embodiment, and a description thereof will be omitted. If the current contrast value Cn + 1 is larger than the previous contrast value Cn in step S206,
That is, if it is in the ascending region of the hill-climbing curve, the process proceeds to step S208, and it is checked whether or not the number n of steps indicating the current lens extension position has reached the closest extension number nmax. Then, if the number nmax of the closest feeding stages has been reached, error processing is performed (step S222), and this program ends. In addition,
The error processing is to stop the motor at the closest feeding end or at an arbitrary position. By the way, the above steps
Steps S208 and S222 and step S212 described below are routines added to the second embodiment.

If it is determined in step S211 that the vehicle is in the descending area of the hill-climbing curve but the number of times of low value detection s has not reached the predetermined natural number m, the process proceeds to step S212. In step S212, the number of steps n indicating the current lens extension position is changed to the closest number n of extension steps.
Compare with max, if it has reached the nearest end, step S221
Moves to the focusing processing operation. Steps S215 to S221 are performed in the second
Since the routine is the same as steps S109 to S115 in the embodiment, description thereof will be omitted.

Finally, a fourth embodiment of the present invention will be described with reference to FIGS. Although FIGS. 9 and 10 are originally one flowchart, step S203 and FIG.
It is described separately between S204. In the third embodiment,
It was not possible to determine whether or not the focusing operation was possible unless the drive was performed up to the closest feeding stage number nmax. However, in the fourth embodiment, it is checked whether or not the focusing detection processing is possible in the middle of the flow, and it is determined that the focusing operation is not possible. If this is the case, the subsequent processing is stopped at that point and the processing is switched to another focusing method (steps S231 and S232). Except for this point, since there is no difference from the third embodiment, the same routines as those in the third embodiment are denoted by the same step numbers, and the description thereof will be omitted. Only different steps S231 and S232 will be described below. .

In step S231, the number nmax of the closest feeding stages
Then, the difference between the lens position and the number n of steps indicating the current lens extension position is obtained, and it is checked whether this difference is smaller than a predetermined natural number m.
If this difference is smaller than m, the low value detection frequency s does not reach the predetermined natural number m even if it is assumed that the low value can be detected in all the lens extension stages from the current position to the closest number of extension stages. The focus detection processing by the hill-climbing method is stopped. Then, the process jumps to step S232 to switch to a process using another focusing method. Other focusing methods include the following. That is, (1) the predetermined natural number m is reduced to reduce the number n m of the nearest feeding stages.
The in-focus detection operation is completed by the time ax is reached, and the lens is driven to the lens release position indicating Cmax.

(2) An error is displayed.

(3) The lens is driven to the final driving stage number position.

(4) Switching to another focus detection method.

In each of the above embodiments, only the luminance information and the flicker information of the subject are handled as the predetermined object having a correlation with the sharpness of the image. A parameter such as FNo, which affects the AF operation, may be added. Also, the predetermined natural number m may be a ROM table corresponding to the above parameter or an arithmetic expression.

According to each of the above embodiments, the predetermined natural number m is changed in accordance with the state of the predetermined object having a correlation with the sharpness of the image, for example, flicker, luminance, and the like, so that accurate and lean climbing is performed. An AF operation using a curve can be performed.

[0036]

As described above, according to the present invention, the signal corresponding to the sharpness of the image obtained by each lens position in the progressive driving of the focusing lens substantially has a peak value. In the auto-focusing system that drives the focusing lens at a position determined to indicate the above, the natural number m when detecting the peak position by comparing the number of times of low value detection s with a predetermined natural number m is defined as the sharpness of the image. Since it is changed in accordance with the state of a predetermined object having a correlation with the above, a remarkable effect that an accurate and lean auto-focusing system can be constituted is exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a hardware configuration of an automatic focusing system according to the present invention.

FIG. 2 is a flowchart of a focusing processing operation in the automatic focusing system according to the first embodiment of the present invention.

FIG. 3 is a flowchart of a subroutine “focusing process” in FIG. 2;

FIG. 4 is another flowchart of a subroutine “focusing process” in FIG. 2;

FIG. 5 is a flowchart of a focusing processing operation in the automatic focusing system according to the second embodiment of the present invention.

FIG. 6 is a flowchart of a focusing processing operation in the automatic focusing system according to the second embodiment of the present invention.

FIG. 7 is a flowchart of a focusing processing operation in the automatic focusing system according to the third embodiment of the present invention.

FIG. 8 is a flowchart of a focusing processing operation in an auto-focusing system according to a third embodiment of the present invention.

FIG. 9 is a flowchart of a focusing processing operation in an auto-focusing system according to a fourth embodiment of the present invention.

FIG. 10 is a flowchart of a focusing processing operation in the automatic focusing system according to the fourth embodiment of the present invention.

FIG. 11 is a focusing curve when the contrast value is flat in the conventional auto-focusing system.

FIG. 12 is a focusing curve when noise is superimposed on a contrast value in a conventional auto-focusing system.

FIG. 13 is a focusing curve in a conventional auto-focusing system when the contrast value changes rapidly.

FIG. 14 is a view for explaining means for determining a predetermined natural number.

Claims (1)

(57) [Claims] 1. A focusing lens according to claim 1, wherein a signal corresponding to the sharpness of an image obtained by each lens in the progressive driving of the focusing lens is determined to substantially show a peak value. An auto-focusing system for driving the focusing lens, wherein first means for determining a predetermined natural number m in accordance with a state of a predetermined object correlated with the sharpness of the image, and sharpening of the image in a process of gradually driving the focusing lens. The focusing lens is gradually driven from the first lens position when the signal level corresponding to the degree indicates the maximum value in comparison with the past to the second lens position by the number of continuous m times determined by the first means. When the signal level falls below the maximum value at each of the lens positions at point m, the first lens position is moved to the focus position. A second means for judging that a signal level corresponding to the sharpness of an image by the focusing lens substantially shows a peak value.